Nanocrystalline oxide powders of the type IrxSn1-xO2 (0.2 <= x <= 1) have been produced and characterised. These oxides have been developed primarily as oxygen evolution electrocatalysts for proton exchange membrane (PEM) water electrolysers. Two methods were used to produce the oxide materials: the modified polyol method and the Adams fusion method. X-ray diffraction analysis suggests that an iridium-tin oxide solid solution with a rutile structure can be produced using the modified polyol method, with a linear relationship between the lattice parameters and composition. The crystal size of the solid solution phase is below 15 nm for all compositions. The Adams fusion method results in at least two separate oxide phases, namely a tin rich oxide and an iridium rich oxide. X-ray photoelectron spectroscopy (XPS) analysis revealed no significant difference between the bulk and surface compositions, and that the iridium, was present in at least two valent states. The electrical resistivity of the powders was compared, and an exponential increase in resistivity with tin addition was found. Overall the resistivity measurements suggest that the limit for tin addition is around 50-60 mol% due to the high ohmic losses expected at higher tin contents in a PEM water electrolyser. (c) 2005 Elsevier B.V. All rights reserved.